of those 2 modems wich is faster better more best for playing xbox games with out lag

The speed of your connection is determined by the speed tier you are paying for, not the "modem". I put "modem" in quotes because the SGB6580 is a modem/router gateway, not just a modem.

If you only plan to use the xbox, then the xbox connected directly to a standard cable modem (such as the SB6141) will be more efficient and will also eliminate NAT which is sometimes a problem with on-line games.

If you have other devices to connect to the Internet, then you will need a router (unless your ISP can supply you with multiple IP addresses), and if you already have a router that you like, using that router behind the SB6141 would be a better choice than using a cable gateway box like the SGB6580.

I have not personally used the SGB6580, but I have in the past used other modem/router gateway boxes, and all of them have had restricted features and performance issues compared to a standard modem and a good quality stand-alone router.

The only advantage of using an ISP issued or controlled gateway box is if you don't have any networking knowledge, and you want your ISP to handle your network configuration (and the SGB6580 has been specifically designed to allow a cable ISP to totally control it).--A well-regulated militia, being necessary to the security of a free State, the right of the people to keep and bear arms shall not be infringed.

When governments fear people, there is liberty. When the people fear the government, there is tyranny.

I'll second NetFixer 's advice... you are usually better off with a simple modem (the SB6141) and a separate router that you own if you need to hook up multiple devices.

There are multiple issues with cable modem gateway devices (built in router/wireless):

Your ISP controls your firmware. If your ISP refuses to push an update to you, and you have problems with any functionality, you are out of luck. The same applies to a basic modem, but there's less to go wrong with those. With your own separate router, you can update the firmware to add functionality or fix bugs (or just replace it if needed).

You can get more features with your own router if that matters to you. Most cable modem gateways include only basic features.

Your ISP can lock you out of certain features - for example, they can disable the wireless if you don't pay for their wireless service (this is evil if you own the modem, but they can do it if they want to).

Cable modems can last for many years. Wireless standards change quicker. The wireless in the modem will probably become outdated before the modem is ready for replacement.

You can put the SBG6580 into bridge mode and use it as a basic cable modem if you ever need to, but honestly it is just easier to stick with a basic modem.